Synthetic surfactant detergents, such as cationic, anionic, amphoteric, and non-ionic surfactants, are used widely in a variety of detergent and cleansing compositions to impart cleansing properties thereto. In addition these synthetic surfactant detergents have been used in personal care compositions including shampoos and washes. In these personal care compositions, it may be desirable to use combinations and levels of surfactants sufficient to achieve relatively high levels of foam volume and/or foam stability.
However, as is recognized in the art, synthetic surfactant detergents tend to be irritating to the skin and eyes. As concentrations of such detergents increase in personal care compositions so as to impart increased cleansing and foaming properties to these compositions, the irritation associated with such compositions also tends to increase, making them undesirable for use on or near the skin and/or eyes.
Attempts to produce milder cleansing compositions have included combining relatively low amounts of anionic surfactants (which tend to be relatively high-foaming but also relatively highly irritating) with relatively lower irritating surfactants such as nonionic and/or amphoteric surfactants. See, e.g. U.S. Pat. No. 4,726,915. Another approach to producing mild cleansing compositions is to associate the anionic surfactants with amphoteric or cationic compounds in order to yield surfactant complexes. See, e.g., U.S. Pat. Nos. 4,443,362; 4,726,915; 4,186,113; and 4,110,263. Disadvantageously, mild cleansing compositions produced via both of such methods tend to suffer from relatively poor foaming and cleansing performance.
It has further been recognized that, for certain uses, consumers desire cleansing compositions to be relatively clear. In particular, clear compositions are often used advantageously to provide an aesthetic indication of purity to the consumer. However, a number of ingredients commonly used in conventional personal care compositions, including, for example, polymeric thickeners, tend to cause the compositions to become cloudy or opaque. It is not readily predictable which combinations of polymers, surfactants and other optional ingredients may be combined to create compositions that are suitable for use as cleansers and also exhibit high clarity.
Another complicating factor with respect to creating clear compositions is that certain polymeric thickeners require higher pH to maintain clarity and stability in personal care compositions.
U.S. Pat. No. 6,897,253 ('253) describes a substantially crosslinked alkali-swellable acrylate copolymer rheology modifier, water, an alkaline material, and an effective amount of surfactant so that a substantially insoluble compound is stabilized or suspended. The disclosed polymeric rheology modifiers do not start to build substantial viscosity until a pH of about 5 or 6 or higher is achieved. To formulate a composition with a lower pH is difficult but '253 discusses a “Back-Acid” thickening method to achieve clear cleansing systems with an acrylate rheology modifier and high surfactant concentrations (greater than about 9.8% actives) at low pH (about pH 4.5-5). This method involves formulating at a higher pH to obtain the appropriate viscosity and stability and then slowly lowering the pH with an organic acid.
US 2008/0113895 sets forth the use of low molecular weight acrylic polymers with the anionic surfactants sodium laureth sulfate and sodium trideceth sulfate for mild cleansing systems. Clear cleansing system are achieved, but only at pH of greater than 6.5
U.S. Pat. No. 7,803,403 describes the use of low molecular weight acrylic polymers for irritation mitigation and points out the difficulty in creating clear cleansing systems with low molecular weight hydrophobically modified polymers. While clear systems are achieved with low molecular weight acrylic polymer combined with either sodium laureth sulfate, sodium trideceth sulfate, or cocamidopropyl betaine, the pH of the compositions must be 6.5.
It is desirable to formulate skin care compositions, including cleansing compositions, to be as mild as possible to the skin and eyes. One way in which to achieve this goal is by having a composition that has pH that is compatible with the skin and eyes. In addition, there is a need for the compositions to exhibit relatively high clarity, desirable foam properties and/or other desirable aesthetic properties. Additional aspects of skin care compositions involve safety and compatible preservative systems.
The ingredients of the skin care compositions of this invention may also require certain pH parameters. For example, certain active ingredients such salicylic acid, require low pH for activity.
Some preservative systems, preservatives that function in their acidic form and not in there salt form, e.g. sodium benzoate or potassium sorbate, require a low composition pH for efficacy. The efficiency of the preservative decreases with increasing pH, dependent upon the pKa of the preservative. Therefore it is desirable to formulate at low pH to provide maximum efficiency while maintaining a pH compatible with the skin and eyes.
Additionally, it is desirable to formulate compositions to have a pH neutral to the skin, from about 5 to about 6. Cleansers having a pH below that of skin (between about 4 and about 5) may be desired in order to lower the pH of skin for enhanced enzyme function and to alter the skin microflora.
The skin care compositions of this invention have low pH yet have high clarity. The compositions have low irritation characteristics and are clear.